EXPRESS: Comprehensive assessment of the cerebral pressure-flow relationship in chronic kidney disease

Chronic kidney disease (CKD) is associated with blood pressure (BP) instability and increased cerebrovascular risk, but how CKD alters cerebral pressure-flow relationship remains unclear. Seventeen adults with moderate to severe CKD and 17 controls completed a multimetric protocol including resting supine recordings to assess spontaneous BP-middle cerebral artery mean blood velocity (MCAv) interactions using wavelet phase synchrony index and Granger based conditional joint transfer entropy, acute BP increases via 3 min isometric handgrip at 30% maximal voluntary contraction, acute BP decreases using sit to stand, and forced ABP oscillations using repeated squat-stands at 0.05 Hz and 0.10 Hz. Mean arterial pressure, MCAv, and end-tidal carbon dioxide partial pressure (PETCO₂) were continuously recorded. Transfer function metrics and MCAv responses to transient mean arterial pressure increases and decreases were comparable between groups. Directional sensitivity was present in both groups at 0.05 Hz only. Wavelet phase synchrony index was elevated in ultra low frequency bands (0.030-0.035 Hz and 0.035-0.040 Hz), and Granger based conditional joint transfer entropy increased by 55% in forward MAP→MCAv information transfer in CKD persisting after PETCO₂ correction. No between-group differences were detected using the linear assessments employed in this study, whereas nonlinear analyses identified differences during spontaneous resting conditions.